test/test_syscalls.c: check unlinked testfiles at the end of the test

test/test_syscalls.c: check unlinked testfiles at the end of the test

On some tests on regular files, open an O_PATH fd of the testfile and
record it along side the size and mode and inode.

At the end of all tests, use recorded testfiles info to re-check the size
mode and inode of the unlinked testfiles.

With O_PATH fd, the server does not have to keep the inode alive so FUSE
inode may be stale or bad.  Therefore, ESTALE and EIO are valid results
for fstat() on the old testfile fd's, but returning the wrong size or
mode is an invalid result.

Signed-off-by: Amir Goldstein <amir73il@gmail.com>